The medial part of the central amygdala is involved in behavioral and physiological conditioned fear responses. Are the different types of fear responses reflected in different associations between behavioral and physiological components? Viviani et al. detected separate neuronal populations with distinct projections to brain stem nuclei in the rat that steer freezing versus cardiovascular function. The neuronal populations in the medial central amygdala also exhibited distinct electrophysiological characteristics and responded differently to oxytocin agonists. In a contextual fear conditioning paradigm, oxytocin selectively affected freezing, but not heart rate variability, which may explain reduced freezing and increased maternal aggression when rats defend their offspring.